Research On Method Of Hierarchical Judgment For Single-phase Grounding Fault In Distribution Network

In China,the power supply system of 10 k V distribution network is mostly a small current grounding system.When the small current grounding distribution system has a single-phase grounding fault,it is allowed to continue to operate for one to two hours.If it runs in this way for a long time,the insulation leve l of the system will be irreversibly damaged,the lines,facilities,and power distribution equipment and other devices associated with the fault line will also be destroied.According to statistics,single-phase grounding fault is the most common fault in distribution network.However,in China,the distribution network has long lines,many branches,and complex wiring.When a single-phase grounding fault occurs in small current grounding system,the correct rate of line selection is low,and it becomes difficult to locate the fault point accurately.Therefore,it is of great significance to locate fault lines and fault points quick ly in order to improve power supply reliability of distribution network.In this paper,combined with the method of single-phase grounding fault in Weihai distribution network,the idea of hierarchical judgment for single-phase grounding fault is proposed.According to the fault line property of single-phase grounding fault and fault location ability,the three-layer detection strategy is used to detect the single-phase grounding fault.The first layer,the grounding fault occurred in the branch line,the automatic dividing switch of distribution network is used to cut the branch line directly from the main line to avoid expanding the range of power outages.The second layer,the grounding fault occurred in the main line,the small current line selection device of the substation is used to detect.The signal obtained by the bus of the substation is used to locate the fault line by analyzing its transient characteristics.By this way,the fault line instead of the fault point can be located.The third layer,the line which need more accurate fault point located,the line selection system of fault indicator of fault recording type is used to test.By the fault indicator installed in distribution network,the detection data of fault line is transmitted right away.With the combination of the transient signal algorithm and neural network method,after the validation of simulation and example,the fault point can be located more accurately.In this way,the area of power failure will be narrowed,so that the power supply reliability will be improved.In this paper,the hierarchy analysis method of single-phase grounding fault line selection and fault point location can adapt to the distribution network environment effectively.According to the important degree of lin es and customers,and the cost performance,the failure analysis of three layers or a layer,or two layers is allocated reasonably.It can be not only used to improve the power supply reliability,but also used to guide to choose the fault testing method i n the new distribution network.